The operation of the centrifugal fan is mainly that the motor drives the impeller, sucks the air into the impeller and sends the air out from the air outlet through centrifugal acceleration, which inevitably causes different amplitudes of vibration. Generally, the vibration amplitude of the centrifugal fan is within the standard range. , but in some cases, the vibration amplitude exceeds the standard. What’s the matter with the large vibration of the centrifugal fan?
1) The reason for the large vibration of the centrifugal fan
1. Uneven wear and surfacing electrodes
During the operation of the centrifugal fan, the impeller is worn by the scouring of the flue gas, and its anti-wear performance can be increased by surfacing the surface of the airfoil blade with wear-resistant welding rod and coating with anti-wear coating. However, due to the uneven wear of each blade, the uneven amount of surfacing electrodes, and the uneven application of anti-wear coatings, it will cause dynamic imbalance after the centrifugal fan is started.
2. Centrifugal fan blades enter ash
Generally, the airfoil blade is hollow, and the hoof-shaped wrap angle and the web are worn by the flue gas, causing the blade to enter the ash. With the accumulation of ash, the center of gravity of the impeller shifts, causing dynamic imbalance and increasing vibration.
3. Inaccurate alignment data for wheel alignment
Due to the self-weight of the rotor of the centrifugal fan, the rotating shaft has a downward deflection. When aligning the wheel, the radial upward runout of the back wheel on the fan side and the upper opening caused by this factor must be considered. and the motor side is low. The alignment standard is 0.2mm lower on the motor side and 0.15mm on the upper opening. If it is completely aligned with the rigid rotor, it will produce large vibration.
4. Thermal bending of the rotor
In the start-up stage of the centrifugal fan unit, the fan runs in a single series, and the rotor of another fan that is not in use will bend the shaft under the heating of the flue gas. According to the actual measurement, even in the state of cranking, the rotor deformation is still large, and the cranking cannot eliminate this deformation. In this way, the center of gravity of the rotor is shifted, causing the centrifugal fan to vibrate beyond the standard when it is restarted, making it unusable.
2）the treatment method of centrifugal fan with large vibration
1. Dynamic balance method
The dynamic imbalance of the centrifugal fan caused by the offset of the center of gravity can be eliminated by adding weight. On the thrust bearing side journal of the centrifugal fan, use white paint to divide the rotor shaft into 12 points in the circumferential direction according to the positions corresponding to the blades (there are 12 blades on the impeller), and mark them with Arabic numerals from 1 to 12.
After the centrifugal fan is started, measure the phase and full-amplitude vibration value with a flash vibrometer. Use the vector method to calculate and confirm the position and weight of the trial weight, and eliminate the dynamic imbalance by adding the weight to the unbalanced position corresponding to the shaft number on the rotor center plate. Usually, the dynamic imbalance problem can be solved after two trial weights.
If the full-amplitude vibration value of the centrifugal fan is 0.18mm and the phase is at 10 points after the centrifugal fan is started, the trial weight and phase are determined by calculation. First add a weight of 1.5kg at 11 o’clock, the measured vibration value is 0.10mm, and the phase is at 8 o’clock. Calculate the added weight and phase required to eliminate vibration from the effect value generated by the trial weight.
2. Hot shaft alignment method
Put into the cranking machine and measure the deflection of the centrifugal fan shaft every half an hour, and place the shaft bending convex point at the apex, carry out the hot-state shaft calibration, and monitor the shaft deflection, and eliminate the shaft deflection value through multiple hot calibrations.
3. Other measures
(1) Check the dust accumulation in the centrifugal blade, and judge whether there is dust accumulation in the blade by rotating the rotor in the cold state to hear whether there is any noise in the blade. If there is dust accumulation, cut the dust accumulation point and release the dust accumulation.
(2) When surfacing the blades and applying anti-wear coatings, try to ensure the uniformity of the amount of surfacing electrodes and coatings for each blade, prevent the appearance of large partial weights, improve the coating process, and prevent the coatings from falling off during operation.
